Crankshaft for an alternative cooling compressor

ABSTRACT

The present invention refers to a crankshaft ( 1 ) for an alternative compressor comprising a main shaft ( 21 ) connected to an eccentric pin ( 2 ) by means of a peripheral flange ( 3 ) containing a lubricating hole ( 24 ) extending through said eccentric pin ( 2 ) and through at least part of the body of main shaft ( 21 ), one of the edges of said hole ( 24 ) being on the cylindrical surface ( 2   a ) of said eccentric pin ( 2 ). With this type of hole, the present invention allows for the use of shafts having extremely low diameters (and, as result, with low viscous loss), even with high eccentricities, whereby an excellent capacity of oil pumping and mechanical strength is maintained.

FIELD OF THE INVENTION

The present invention refers to a crankshaft for an alternative coolingcompressor having an improved lubrication hole.

BASIS FOR THE INVENTION

A compression has the function of increasing the pressure of adetermined fluid volume to a pressure required for carrying out arefrigeration cycle.

FIG. 1 schematically illustrates the main parts of mobile assembly of analternative-type cooling compressor, wherein a connecting rod/cranksystem is used to convert rotary movement of electric motor toalternative movement of a plunger.

Thus, FIG. 1 illustrates a main shaft (or shaft body) 1 connected to aneccentric pin 2 by means of flange 3. Eccentric pin 2 is connected bymeans of a connecting rod 4 to a plunger 5 that moves within cylinder 6a of a cylinder block 6. The assembly is driven by electric motor 7,wherein a pump 8 secured to shaft 1 or rotor 7 a of electric motor 7feeds the assembly with lubricating oil 9.

Refrigeration industry is highly concerned with the performance ofcooling compressors. In fact, many works and studies have been carriedout to improve this performance, mainly those aiming at reducingmechanical losses of moving parts, such as those generated on radialbearings of a compressor.

Mechanical loss in radial bearings is generated by contact betweensurfaces of parts and viscous friction resulting from the presence oflubricating oil.

Losses caused by contact of surfaces of shaft and bearing follow theequation given below:

Pot=Fa×ω×R, where Fa=μμN,

wherein

Pot=friction-generated potency;

Fa=friction force;

ω=relative angular velocity;

R=shaft radius;

μ=dynamic friction coefficient; and

N=normal force.

Viscous friction losses (from shearing of lubricating oil due to themovement between shaft and bearing) follow the equation below:

Pot: cte×f(ω)×(η×ω²×R³×L)/c

wherein

Pot=friction-generated potency;

ω=relative velocity between surfaces;

η=oil viscosity;

R=shaft radius;

L=useful width of bearing.

c=radial clearance between surfaces; and

ε=shaft/bearing eccentricity ratio

To reduce these mechanical losses, solutions are known from the statethe art, which involve altering the geometry of component parts toreduce friction. Among this type of solution, it can be mentioned thepossibility of reducing the diameter of the shaft and eccentric pin.

As reduction in viscous loss is proportional to the cube of the shaftradius, reduction in bearing diameter is one of the most interestingalternatives to reduce mechanical loss in a bearing.

Nevertheless, there some technical difficulties associated with thiscontinuous reduction in diameter of the main shaft body and eccentricpin, such as:

a) Reduction in the inertial moment and, consequently, strength of theshaft reduces;

b) Reduction in the capacity of centrifugal pumping of an oil, due tothe reduction in the shaft diameter, causes reduction in maximum radiusof oil centrifugation; and

c) Reduction in the capacity of pumping oil in a transition regionbetween shaft body and eccentric pin.

In order to decrease such difficulties associated with item (a), it ispossible, for example, to manufacture a crankshaft from a materialhaving higher mechanical strength, such as nodular cast iron or steel.

With regard to the difficulties associated with item (b) above, it ispossible to overcome same by, for example, opting to resort to asolution suggested in U.S. Pat. No. 6,416,296 B1.

With regard to the difficulties associated with item (c) above, they arein fact a technical limitation in reducing diameters of the main shaftand eccentric pin, mainly when associated with elevated values ofeccentricities of eccentric pin, because the space available formachining a lubrication hole (responsible for transferring oil betweenthe shaft body and eccentric pin) is highly limited.

Shaft holes known in the art usually have two main configurations asshown in FIGS. 2 and 3.

In FIG. 2, the configuration comprises a hole 10 beginning on face 2 aof a cylinder defining eccentric pin 2 and goes towards the center ofthe body of main shaft 1 until reaching a hole 11 transversal togeometric shaft of shaft 1.

Such a configuration has a limitation with respect to oil pumpingprocess, because to transfer the oil from the lubricating channel of themain shaft body to the eccentric pin, it is required that same is forcedto flow towards the body center, in an opposite direction to thecentrifugal force generated by shaft rotation. Thus, in saidconfiguration, the oil volume transferred to eccentric pin is inverselyproportional to the maximum radial depth “E” to which oil is forcedagainst centrifugal force (depth of hole 11 in radial direction).

With regard to the configuration depicted in FIG. 3, a hole of eccentricpin 2 terminates into a position directly interlinking with lubricatingchannel 12 of main shaft body 1 (helical channel that defines a surfacechannel commonly used in part of the process for pumping oil from thecompressor reservoir). This configuration, although eliminating saidproblem associated with the process for pumping oil in an oppositedirection to centrifugal force, shows a better performance when an axialbearing is flat, which acts as a mechanical sealing thus avoiding thatoil is totally expelled from the shaft when lubricating channel of theshaft body is not covered by a block radial bearing. That is, thisconfiguration is effective when said axial bearing prevents or restrictsleakage of oil that would be expelled from the shaft by centrifugalforce of the action.

Although there are solutions using the solutions discussed above asbasis for minor changes in a design, geometrical complexities of suchholes and their processes increase when a combination of diameters ofshaft and eccentric pin of values below 14 mm and eccentricities above8.0 mm is used.

OBJECTS OF THE INVENTION

Therefore, one object of the present invention is to provide a coolingcompressor shaft having a hole that allows for a significant reductionin the dimensions of the crankshaft without substantially restrictingthe eccentricity of eccentric pin and minimally restricting the oilvolume pumped to eccentric pin and plunger.

SUMMARY OF THE INVENTION

The above-mentioned objects of the present invention are accomplished bymeans of a crankshaft for a cooling compressor which usually comprises amain shaft (or shaft body) connected to an eccentric pin and having alubricating hole extending through said eccentric pin and through atleast part of the main shaft body, wherein one of the hole edges is onthe cylindrical surface of the eccentric pin and the hole center line iscontained in a plane B-B that does not comprise a geometric shaftpassing through the center line of the main shaft body and is rotated ata angle “B” in relation to plane P defined by the center lines of themain shaft body and eccentric pin, which configuration permits providinga hole with minimum restriction to oil pumping and suitable wallthicknesses. In a preferred embodiment of the invention, the main shaftand eccentric pin are connected by means of a peripheral flange whichusually defines axial bearing (and which also usually incorporates acounterweight mass). However, in an alternative embodiment of thepresent invention, the main shaft body is directly connected to theeccentric pin with no peripheral flange.

Further, in the preferred embodiment of the present invention, the otheredge of the hole is on the cylindrical shaft body surface. However, inan alternative embodiment, the other edge of the hole is inside theshaft body, and a complementary hole connects this edge to thecylindrical shaft body surface. In another alternative embodiment, theother edge of the hole is totally on the surface of the peripheral axialseat flange or on a region intermediate the axial seat and cylindricalshaft body surface generating a groove in a portion of said surface.

Additionally, any of the solutions presented herein are also suitablefor crankshafts in which an eccentric pin is disposed between 2 bearingsof a bi-bearing crankshaft.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a schematic view showing main parts of the mobileassembly of an alternative-type cooling compressor;

FIG. 2 illustrates a cut view of the edge of a conventional compressorcrankshaft at which an eccentric pin is disposed;

FIG. 3 illustrates a cut view of the edge of another type of aconventional compressor crankshaft at which an eccentric pin isdisposed.

FIG. 4 illustrates a top view of a compressor crankshaft in accordancewith a preferred embodiment of the present invention;

FIG. 5 illustrates a cut view, indicated in FIG. 4, of the edge of acompressor shaft at which the eccentric pin in accordance with thepreferred embodiment of the present invention is disposed;

FIG. 6 illustrates a cut view of the edge of a compressor shaft at whichan eccentric pin in accordance with an alternative embodiment of thepresent invention is disposed;

FIG. 7 illustrates a top view of a compressor crankshaft in accordancewith an alternative embodiment of the present invention.

FIG. 8 illustrates a cut view, indicated in FIG. 7, of the edge of acompressor shaft at which an eccentric pin in accordance with thealternative embodiment of the present invention is disposed;

FIG. 9 illustrates a graph showing experimental results of measuring anoil leakage (pumping capacity) of a shaft, wherein the maximal depth oflubricating hole 24 in relation to the shaft body surface (“E”) has beenvaried;

FIG. 10 illustrates a graph showing the result of a technical study for4 different eccentricities of an eccentric pin, in which hole 24 wasmaintained fixed in relation to the body shaft.

DETAILED DESCRIPTION OF THE INVENTION

Next, the present invention will be described in more details based onexecution examples represented in the drawings. It is to be construedthat the principles of the present invention can be applied to any type,size or configuration of an alternative compressor.

FIGS. 4 and 5 show a preferred embodiment of the crankshaft of thepresent invention, wherein FIG. 4 is a top view and FIG. 5 is a partialcut view of edge portion of the shaft at which an eccentric pin isdisposed.

As can be seen from these figures, crankshaft 1 of the present inventioncomprises a main shaft 21 connected to an eccentric pin 2 by means of aperipheral flange 3.

Nevertheless, it should be observed that the presence of this flange isnot necessary, wherein in other embodiments of the present invention themain shaft can be directly connected to the eccentric pin. Aconstruction of these types of shafts is well known from the state ofthe art, and the function thereof has been formerly commented.

To avoid problems and drawbacks associated with the solutions for holesof the state of the art, the crankshaft 1 of the present inventioncomprises a hole 24 which edge begins (or terminated, depending on theused machining technique) on the cylindrical surface 2 b of pin 2, andterminates (or begins, depending on the used machining technique) on thecylindrical surface 21 a of the body of main crankshaft 21, as can beseen from FIGS. 4 and 5.

A helical lubricating channel (not shown) is provided on the cylindricalsurface 21 a of main shaft 21. Said lubricating channel is known fromthose skilled in the art and, therefore, it will not be described indetail herein.

In the preferred embodiment shown in FIGS. 4 and 5, hole 24 is in aplane B-B that does not contain a geometric shaft passing through thecenter line of main shaft 21 and is rotated at an angle “B” to plane Bdefined by the center lines of main shaft 21 and of eccentric pin 2 tominimize the maximum depth “E” of the inner surface of hole 24 relativeto the cylindrical surface 21 a of main shaft 21.

Therefore, by minimizing the maximum depth “E” (or maximizing theminimum radius “R1”), a lower restriction to the flowing of oil fromsaid main shaft 21 to eccentric pin 2 is obtained. Hence, using a holeconfiguration of the present invention, a high degree of flexibility atthe position of hole 24 is achieved, where a maximum radial depth “E”(values below 4.0 mm) can be obtained by correctly combining angles “B”and “D” (“D” being an angle at the starting position of hole 24 on thesurface 2 b of eccentric pin), when the dimensions given by eccentricity“A”, diameter “F” of hole 24 and diameters of main shaft 21 andeccentric pin 2 of the crankshaft 1 are considered.

The benefit attained by increasing the minimum radius “R1” (or reducingthe maximum radial depth “E”) to the oil flow rate can be seen fromFigure, which shows

Next, the present invention will be described in more details based onexecution examples represented in the drawings. It is to be construedthat the principles of the present invention can be applied to any type,size or configuration of an alternative compressor.

FIGS. 4 and 5 show a preferred embodiment of the crankshaft of thepresent invention, wherein FIG. 4 is a top view and FIG. 5 is a partialcut view of edge portion of the shaft at which an eccentric pin isdisposed.

As can be seen from these figures, crankshaft 1 of the present inventioncomprises a main shaft 21 connected to an eccentric pin 2 by means of aperipheral flange 3.

Nevertheless, it should be observed that the presence of this flange isnot necessary, wherein in other embodiments of the present invention themain shaft can be directly connected to the eccentric pin. Aconstruction of these types of shafts is well known from the state ofthe art, and the function thereof has been formerly commented.

To avoid problems and drawbacks associated with the solutions for holesof the state of the art, the crankshaft 1 of the present inventioncomprises a hole 24 which edge begins (or terminated, depending on theused machining technique) on the cylindrical surface 2 b of pin 2, andterminates (or begins, depending on the used machining technique) on thecylindrical surface 21 a of the body of main crankshaft 21, as can beseen from FIGS. 4 and 5.

A helical lubricating channel (not shown) is provided on the cylindricalsurface 21 a of main shaft 21. Said lubricating channel is known fromthose skilled in the art and, therefore, it will not be described indetail herein.

In the preferred embodiment shown in FIGS. 4 and 5, hole 24 is in aplane B-B that does not contain a geometric shaft passing through thecenter line of main shaft 21 and is rotated at an angle “B” to plane Bdefined by the center lines of main shaft 21 and of eccentric pin 2 tominimize the maximum depth “E” of the inner surface of hole 24 relativeto the cylindrical surface 21 a of main shaft 21.

Therefore, by minimizing the maximum depth “E” (or maximizing theminimum radius “R1”), a lower restriction to the flowing of oil fromsaid main shaft 21 to eccentric pin 2 is obtained.

Hence, using a hole configuration of the present invention, a highdegree of flexibility at the position of hole 24 is achieved, where amaximum radial depth “E” (values below 4.0 mm) can be obtained bycorrectly combining angles “B” and “D” (“D” being an angle at thestarting position of hole 24 on the surface 2 b of eccentric pin), whenthe dimensions given by eccentricity “A”, diameter “F” of hole 24 anddiameters of main shaft 21 and eccentric pin 2 of the crankshaft 1 areconsidered.

The benefit attained by increasing the minimum radius “R1” (or reducingthe maximum radial depth “E”) to the oil flow rate can be seen fromFigure, which shows inversely proportional ratio between reduction inthe maximum radial depth “E” and increase in the oil flow rate.

In order to achieve a correct machining of a hole 24, in accordance withthe preferred embodiment of the invention, the drilling tool must beintroduced from a angle “D” in relation to the center of the eccentricpin, and, in plane B-B, the hole 24 has an inclination at angle “T” inrelation to the center line of the main shaft 21, wherein such angles(“D” and “T”) are defined by:

-   -   eccentricity “A” of the eccentric pin;    -   diameter of main shaft 21 and eccentric pin 2; and    -   axial distance between the beginning and end (“H” and “C”        heights) of the hole on the surfaces of main shaft 21 and        eccentric pin 2.

The beginning of the hole on the cylindrical surface 2 b of eccentricpin 2 permits using angles “I” of about 45°, which, in combination withangle “B”. allows for said hole to be disposed in a region which ensuressatisfactory wall thicknesses (“esp1” and “esp2” in FIG. 5, above 1.0mm) even with the use of shafts having:

-   -   diameter of body and eccentric pin less than 14.0 mm;    -   diameters of hole “F” of 2.5 mm or greater;    -   eccentricities of 12.00 mm or greater;    -   reduced thicknesses in peripheral flange defining axial seat.

Upon analyzing the manufacture process required for machining said hole24, taking into account that shafts having different eccentricities inthe same equipment are produced, it is possible to simplify this process(time reduction in the preparation of machines or setup) by maintaininga fixed position of hole 24 in relation to the shaft body 21 for adetermined range of eccentricities “A”.

As depicted in FIG. 4, by maintaining angle “B” and minimum radius “RO”fixed, the starting position of hole 24 on the surface of eccentric pin2 b defined by angle “D”, turns out to be variable with eccentricity“A”. FIG. 8 shows this situation for different eccentricities(eccentricities 6, 8, 10 and 12 mm).

FIG. 6 shows an alternative embodiment of the present invention, wherehole 24 is not a hole that entirely passes through main shaft 21 ofcrankshaft 1. In this sense, FIG. 6 illustrates crankshaft in a cut viewcorresponding to cut B-B shown in the embodiment of FIG. 4.

In this case, it is used a complementary hole 25 interconnecting hole 24with a helical channel on the surface of main shaft 21.

Said complementary hole 25 can be perpendicular to the surface of mainshaft 21, as shown in FIG. 6, or can have another type of suitabledirection.

Additionally, in another alternative embodiment, as illustrated in FIGS.7 and 8, hole 24 can totally or partially terminate on the axial surface3 a of peripheral flange 3 similarly to the termination of thelubricating hole depicted in FIG. 3. Maximum depth “E” becomes zerobecause minimum radius “R1” is greater than radius “Rc” of the body ofmain shaft 21, and, consequently, there will be no more need to ensure aminimum thickness“esp.2”.

For this particular configuration in which hole 24 partially reaches themain shaft body, said hole 24 is no longer completely formed in thisregion and then it passes to form a (semi-cylindrical) channel over thecylindrical surface 21 a of the body of main shaft 21, which can bedirectly connected to a helical lubricating channel normally disposed atsaid shafts. Additionally, the present invention is not only applicableto crankshafts with eccentric pin axially disposed at one of the edgesof the main body, wherein it can also be used in crankshafts at which aneccentric pin is disposed between 2 bearings of a bi-bearing crankshaft.

The present invention allows for a high degree of flexibility on thedesign of a hole of a compressor crankshaft to be obtained, the presentinvention permitting:

-   -   increasing the thicknesses (“esp.1” and “esp.2”) of the shaft        wall thus ensuring a maximum radial depth “E” suitable for an        oil pumping process; and    -   disposing the beginning and the end of the hole in a region        outside the bearing load (region where more pressures on the        lubricating film during hydrodynamic regime are produced);    -   simplifying the machining process (reduction in the time of        machining preparation or setup), whereby a fixed position of        hole 24 in relation to the body of shaft 21 for a determined        range of eccentricities “A” is maintained.

In fact, the present invention provides for the use of crankshaftshaving extremely low diameters (and, consequently, having low viscousloss) even with high eccentricities (12.0 mm or above) therebymaintaining an excellent capacity of oil pumping, mechanical strengthand being easy to fabricate.

It should be understood that the description provided based on thefigures above only refers to possible embodiments for the crankshaft ofthe present invention, where the true scope of the object of the presentinvention is defined by the appended claims.

1. Crankshaft (1) for an alternative compressor comprising a main shaft(21) connected to an eccentric pin (2) and a lubricating hole (24)extending through said eccentric pin (2) and through at least part ofthe body of main shaft (21), CHARACTERIZED in that one of the edges ofsaid hole (24) is on the cylindrical surface (2 b) of the eccentric pin(2), where said hole (24) is contained in a plane B-B that does notcontain a geometrical shaft passing by the center line of main shaft(21) and is rotated at an angle “B” relative to plane P defined by thecenter liners of main shaft (21) and eccentric pin (2) ensuring amaximum radial depth “E” of 4.0 mm of the inner surface of hole (24)relative to the cylindrical surface (21 a) of main body (21). 2.Crankshaft (1), in accordance with claim 1, CHARACTERIZED in that ituses a hole having minimum wall thicknesses (“esp.1” and “esp.2”) of1.00 mm.
 3. Crankshaft (1), in accordance with claim 1 or 2,CHARACTERIZED in that said main shaft (21) is directly connected toeccentric pin (2).
 4. Crankshaft (1), in accordance with claim 1 or 2,CHARACTERIZED in that said main shaft (21) is connected to eccentric pin(2) by means of a peripheral flange (3).
 5. Crankshaft (1), inaccordance with any of claims 1 to 4, CHARACTERIZED in that the otheredge of hole (24) is on the cylindrical surface (21 a) of the body ofmain shaft (21).
 6. Crankshaft (1), in accordance with any of claims 1to 4, CHARACTERIZED in that the other edge of hole (24) is inside thebody of main shaft (21), and a complementary hole (25) connects saidedge to the cylindrical surface (21 a) of the body of main shaft (21).7. Crankshaft (1), in accordance with claim 4, CHARACTERIZED in that theother edge of hole (24) terminates totally or partially on the axialsurface (3 a) of peripheral flange (3).
 8. Alternative compressor havinga crankshaft comprising a main shaft (21) connected to an eccentric pin(2) and a lubricating hole (21) extending through said eccentric pin (2)and through at least part of the body of main shaft (21), CHARACTERIZEDin that one of the edges of said hole (24) is on the cylindrical surface(2 b) of the eccentric pin (2), where said hole (24) is contained in aplane B-B that does not contain geometrical shaft passing by the centerline of main shaft (21) and is rotated at an angle “B” relative to planeP defined by the center liners of the main shaft (21) and eccentric pin(2) ensuring a maximum radial depth “E” of 4.0 mm of the inner surfaceof hole (24) relative to the cylindrical surface (21 a) of main body(21).
 9. Alternative compressor, in accordance with claim 8,CHARACTERIZED in that it uses a hole having minimum wall thicknesses(“esp.1” and “esp.2”) of 1.00 mm.
 10. Alternative compressor, inaccordance with claim 8 or 9, CHARACTERIZED in that said main shaft (21)is directly connected with the eccentric pin (2).
 11. Alternativecompressor, in accordance with claim 8 or 9, CHARACTERIZED in that saidmain shaft (21) is connected to the eccentric pin (2) by means of aperipheral flange (3).
 12. Alternative compressor, in accordance withany of claims 8 to 11, CHARACTERIZED in that the other edge of hole (24)is on the cylindrical surface (21 a) of the body of main shaft (21). 13.Alternative compressor, in accordance with any of claims 9 to 11,CHARACTERIZED in that the other edge of hole (24) is inside the body ofmain shaft (21), and a complementary hole (25) connects said edge to thecylindrical surface (21 a) of the body of main shaft (21). 14.Alternative compressor, in accordance with claim 11, CHARACTERIZED inthat the other edge of hole (24) terminates totally or partially on theaxial surface (3 a) of peripheral flange (3).